Hearing is one of the most important sensations that people need for daily life. With hearing, we can communicate with people, enjoy beautiful music, and fulfill our everyday needs. However, as people are aging, hearing loss seems an inevitable experience. According to Wingfield and Peelle (2012), 40–50% of adults over the age of 65 years have a measurable hearing impairment, with this figure rising to 83% of those over the age of 70 years. These data make hearing loss the third most prevalent chronic medical condition among older adults. Both of my grandparents have experienced serious hearing damage since turning eighty. When I talk to them, they always have a hard time understanding what I say. I feel that every year, the distance when I talk to them becomes closer and closer. At the dinner table, I always see their confusing eyes trying hard to understand what people say which is heartbreaking.
This is the type of hearing aid that my grandparents are using.
The reason for hearing loss behind aging is the loss of hair cells located on the basilar membrane in the cochlea in the inner ear which transduce the mechanical vibrations into neural impulses that reach the primary auditory cortex via the eighth cranial nerve. Loss of hair cells in the region of the basilar membrane is responsive to the high-frequency sounds that are critically important for the perception of speech. Therefore, elders like my grandparents would have problems during communication. A recent study has used MRI to examine brain activity while participants listened to sentences that varied in their grammatical complexity. The listeners with poorer hearing showed a smaller degree of change in their neural activity for the more complex sentences relative to the less complex ones in brain regions. Therefore, the conclusion is drawn that hearing loss can inflate the appearance of cognitive decline in older adults (Wingfield and Peelle 2012). Loss of hearing not only impacts people’s ears, but also the cognitive part of the auditory system which is the brain.
However, on the other hand, not all deafness is damaged after people get older. Prelingual deafness, referring to deafness that occurs before learning speech or language, is possible as well. While deafness influences the cognitive function of old adults which is difficult to recover and develop a substitute to compensate for the loss, prelingual deaf children induce plastic alterations in the functional-neuroanatomical organization of the conceptual system. Researchers propose that the lack of auditory information might be compensated by the increased importance of verbal associations stored in the language systems (Trumpp and Kiefer 2018). The study recruited sixteen prelingually deaf participants and eighteen healthy hearing volunteers. Using functional magnetic resonance imaging, researchers found additionally enhanced activation in visual and motor areas of deaf versus hearing participants, suggesting that the loss of the auditory channel is partially compensated by the increased importance of visual and motor information for constituting object knowledge. Therefore, results indicate that conceptual processing in deaf compared to hearing people is more strongly based on the language system, complemented by an enhanced contribution of the visuo-motor system (Trumpp and Kiefer 2018). Although deafness is an unfortunate disability, the brain activates extra regions to satisfy people’s daily work and needs.
In contrast to becoming deaf during old age, prelingual deafness is luckier. If people have barely experienced hearing sound, it would not be a huge discrepancy. However, gradually losing sound and failing to experience what people have experienced before would be more of torture. Moreover, we, who are healthy and able to enjoy the beauty of sound should appreciate how lucky we are because maybe we will lose hearing one day as we get older like our grandparents. Have conversations, listen to music, and appreciate all sounds we could hear!
References:
Trumpp, N. M., & Kiefer, M. 2018. Functional reorganization of the conceptual brain system after deafness in early childhood [Internet]. PloS one [cited 2020 Nov 22]. Available from: https://doi.org/10.1371/journal.pone.0198894
Wingfield, A., & Peelle, J. E. 2012. How does hearing loss affect the brain? [Internet]. Aging health [cited 2020 Nov 22]. Available from: https://doi.org/10.2217/AHE.12.5
Hi Lydia, this is a really amazing post. I have always thought that pre-lingual deafness was a very hard thing for people to endure, but it seems that post-lingual is much worse as they have accustomed to one way of life. I thought it was really cool how the brain’s neuro-plasticity can work in ways to compensate for one of our main sense which nature has deemed evolutionarily necessary. More power to the brain!